Recently, there are various image forming methods such as silver halide photography, electrophotography, thermal transfer recording methods, and inkjet recording methods. Among these image forming methods, inkjet recording methods are used for various printing fields such as plain paper printing, photographic image printing, marking, color filter formation, and the like because of being capable of producing images at low costs. Inkjet recording methods are broadly classified into aqueous-ink type inkjet recording methods using an aqueous ink, solvent-ink type inkjet recording methods using a solvent ink which includes a quick-drying organic solvent so as to be dried quickly, photocrosslinking-ink type inkjet recording methods in which a recorded image is irradiated with ultraviolet light to be crosslinked, and thermofusible-ink type inkjet recording methods which include heating an ink which is solid at room temperature to liquefy the ink, and then ejecting the liquefied ink to form an image.
The photocrosslinking-ink type inkjet recording methods have advantages over the solvent-ink type inkjet recording methods that odor is less, the drying speed is faster, and images can be recorded even on recording materials which hardly absorb ink.
There is a proposal for an ultraviolet crosslinking inkjet ink which includes an oxetane compound or an alicyclic epoxy compound, and an (meth)acrylate compound and which further includes a photo-acid generator in an amount of from 1% to 10% by weight and a photoradical generator in an amount of from 0 to 1% by weight.
However, when the ink includes a photoradical generator capable of crosslinking the ink when using a light emitting diode (LED), the ink typically causes a problem in that images formed by the ink are yellowed (hereinafter referred to as a yellowing problem).
For these reasons, the inventors recognized that there is a need for an ultraviolet crosslinking ink which includes a photoradical generator capable of crosslinking the ink when using a light emitting diode (LED) but which does not cause the yellowing problem.